Damping enhancement in coherent ferrite/insulating-paramagnet bilayers

TL;DR

This study reveals that chemical disorder at oxide interfaces significantly increases magnetic damping in ferrite heterostructures, impacting their spin dynamic properties for spintronic applications.

Contribution

It demonstrates that interfacial chemical disorder, not spin pumping, is the main cause of damping enhancement in ferrite/paramagnet heterostructures.

Findings

Damping in MAFO/CCO is over three times higher than in MAFO alone.

Damping enhancement is independent of CCO overlayer thickness.

Interfacial chemical disorder, not spin pumping, causes damping increase.

Abstract

High-quality epitaxial ferrites, such as low-damping MgAl-ferrite (MAFO), are promising nanoscale building blocks for all-oxide heterostructures driven by pure spin current. However, the impact of oxide interfaces on spin dynamics in such heterostructures remains an open question. Here, we investigate the spin dynamics and chemical and magnetic depth profiles of 15-nm-thick MAFO coherently interfaced with an isostructural $\approx$1-8-nm-thick overlayer of paramagnetic CoCr$_2$O$_4$ (CCO) as an all-oxide model system. Compared to MAFO without an overlayer, effective Gilbert damping in MAFO/CCO is enhanced by a factor of $>$3, irrespective of the CCO overlayer thickness. We attribute this damping enhancement to spin scattering at the $\sim$1-nm-thick chemically disordered layer at the MAFO/CCO interface, rather than spin pumping or proximity-induced magnetism. Our results indicate that damping in ferrite-based heterostructures is strongly influenced by interfacial chemical disorder, even if the thickness of the disordered layer is a small fraction of the ferrite thickness.